XNA for Fun and Profit

St Bede’s College

Rob Miles

Department of Computer Science

University of Hull

2

Agenda

• Computer Games

– How Computer Games work

• XNA

– What is XNA?– The XNA Framework– Very Silly Games– Making a game in sixty minutes

• Why everyone should be writing games!

3

The Video Game Business

• Bigger than the movies?

– GTA4 sales topped half a billion dollars in its first week of release, 5 times the earnings of the Iron Man movie

• Set to grow even more?

– It is now easy (and cheap) to write a game in your bedroom and make it available to every Xbox Live subscriber in the world

– The games industry is looking for new kind of games

4

• Games that are very silly and sociable

• Easy to create and understand

• Mainly for multiple players

• Some games are “Zero Graphics”

• Based on examples in:

Learn Programming Now! with Microsoft® XNA™ Game Studio 3.0

by

Rob Miles

“Hide the Gamepad”

6

Sample XNA 2D game“Bread and Cheese”

• We are going to make a simple “casual” game

• The player guides the cheese around with the bread, hitting the tomatoes but avoiding the peppers and tangerines

• This is a simple, 2D, sprite based game

“Bread and Cheese”

8

Computer Game Construction

• Every game that has ever been written does these things:

1. Initialise all the resources at the start

• This is where the “Loading” screen comes from

2. Repeatedly runs the game loop:

a) Update the game world

• read the controllers, update the state and position of the things in the game

b) Draw the game word for the player to see

• Display the game elements on the screen

9

Starting with our Cheese

• To begin writing our game we can make some cheese bounce around the screen

• To draw some cheese the game needs to remember two things

– The picture to draw– The position on the screen to draw it

• In programs these are called variables

Texture2D cheeseTexture;

Rectangle cheeseRectangle;

10

Games and Resources

• Modern games contain thousands of content items:

– Pictures – Sounds– 3D models– Scripts

• A game has to manage all these items so that the program can find and use them cheeseTexture =

Content.Load<Texture2D>("Cheese");

11

Loading the Cheese Texture

• A game is made up of things that hold information (the variables) and things that do stuff (the methods)

• LoadContent is a method that is called when our game

starts running

• It loads our cheese texture and makes it available for use in the game

protected override void LoadContent()

{

cheeseTexture = Content.Load<Texture2D>("Cheese");

cheeseRectangle = new Rectangle (0, 0, 100,100);

}

12

Games and Rectangles

• The Rectangle tells us where on the screen the texture is to be drawn

• It gives the position and the size of the draw operation

Creating a Bank Class

x,y

width

height

13

Positioning the Cheese Texture

• This will draw our cheese image at the top left hand corner and the cheese will be 100 pixels wide and 100 pixels high

• Unlike graph paper, with computer graphics the position of (0,0) is the top left hand corner of the screen

– Increasing the value of Y moves the rectangle down– Increasing the value of X moves the rectangle across

protected override void LoadContent()

{

cheeseTexture = Content.Load<Texture2D>("Cheese");

cheeseRectangle = new Rectangle (0, 0, 100,100);

}

14

Drawing the Game World

• Now we have our cheese we want to draw it for the player to see

• The game contains a Draw method that is called draw the game display on the screen

• We need to add some program code to tell draw to put our cheese on the screen

• This code will send commands to the Graphics Card in the computer to make it draw the texture

Creating a Bank Class

15

XNA Game Drawing

protected override void Draw(GameTime gameTime)

{

graphics.GraphicsDevice.Clear(Color.CornflowerBlue);

spriteBatch.Begin();

spriteBatch.Draw(cheeseTexture, cheeseRectangle,

Color.White );

spriteBatch.End();

base.Draw(gameTime);

}

• This version of the Draw method clears the screen to blue and then draws the cheese

“Cheese Drawing”

Making things move with the Update method

• At the moment the cheese is always drawn at the same place

• We need to make it move about the screen

• Games do this by having an Update behaviour that makes the game world work

– In a racing game this means moving all the cars on the track, checking for collisions etc

– In a shooting game this means moving all the players, checking to see if any bullets have hit anything etc

• At the moment we are just going to make our cheese move

18

Stupid XNA Game Update

• We have two integer variables that hold the speed of our cheese

• They are used to update the position of the cheese rectangle when Update is called

int cheeseXSpeed = 3;

int cheeseYSpeed = 3;

protected override void Update()

{

cheeseRectangle.X = cheeseRectangle.X + cheeseXSpeed;

cheeseRectangle.Y = cheeseRectangle.Y + cheeseYSpeed;

}

“Cheese Moving”

20

Adding some Bounce to the Cheese

• We want the cheese to bounce off the edge of the screen

• We can do this by changing the sign of the speed value

protected override void Update()

{

cheeseRectangle.X = cheeseRectangle.X + cheeseXSpeed;

if (cheeseRectangle.X < 0 ||

cheeseRectangle.Right > GraphicsDevice.Viewport.Width)

{

cheeseXSpeed = cheeseXSpeed * -1;

}

// Repeat for Y

}

“Cheese Bouncing”

22

Creating a bread bat

• Now we need to create a bat texture and then allow the player to control it

• XNA provides support for keyboard and XBOX 360 gamepad

– You can plug a wired gamepad into an PC and it will just work

– You can also get a USB adapter so you can use wireless gamepads

• The gamepad buttons can be tested during the update method

23

XNA Digital Gamepad Input

GamePadState padState = GamePad.GetState(PlayerIndex.One);

if (padState.IsConnected)

{

if (padState.DPad.Left == ButtonState.Pressed)

{

breadRectangle.X = breadRectangle.X - breadSpeed;

}

if (padState.DPad.Right == ButtonState.Pressed)

{

breadRectangle.X = breadRectangle.X + breadSpeed;

}

/// repeat for bread Y position

}

24

XNA Analogue Gamepad Input

• This code uses the analogue input of the left thumbstick to update the position of the bread rectangle

int padXSpeed = 10;

int padYSpeed = 10;

if (pad.IsConnected)

{

breadRectangle.X +=

(int) (pad.ThumbSticks.Left.X * padXSpeed);

breadRectangle.Y -=

(int) (pad.ThumbSticks.Left.Y * padYSpeed);

}

25

Hitting the Cheese

• This code reverses the vertical direction of the cheese when it hits the bread

• It works by detecting when the cheese and bread rectangles intersect

• This is a very simple kind of collision detection

if ( breadRectangle.Intersects(cheeseRectangle))

{

cheeseYSpeed = cheeseYSpeed * -1;

}

26

Adding Sound

• The sound effect is a WAV file

// Sound effect variable

SoundEffect ding;

// Load the sound effect content in LoadContent

ding = Content.Load<SoundEffect>("Ding");

// Play the sound effect when the bread hits the cheese

if ( breadRectangle.Intersects(cheeseRectangle))

{

cheeseYSpeed *= -1;

ding.Play();

}

27

Playing Music

• The Music resource is an MP3 file

• Can also play WMA files and music from the media on the device

// Song variable

Song music;

// Load the song content in LoadContent

music = Content.Load<Song>("Music");

// Play the song using the Media Player

MediaPlayer.Play(music);

“Bread and Cheese”Rob Miles

29

Getting Started with XNA

• All the software is free:

– Visual Studio 2008 Express Edition– XNA Game Studio 3.1

• Games can be run on the XBOX 360

– You need to join the "Creators Club" in order to do this– Students can get free membership through DreamSpark

• Visit robmiles.com for details on how to get started

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Selling your Games

• You can put your XNA games onto Xbox Live

• All Xbox Live subscribers are able to download and play XNA games you have written

• You can even charge money for them

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Summary

• The XNA Framework provides a very powerful environment for game creation

– Write games for your Xbox or PC in C# using Visual Studio

• You should all be writing games

– It is easy to do– It is fun!– You might make some money!

32

Resources

• XNA Creators Club:

http://creators.xna.com/

• DreamSpark

https://downloads.channel8.msdn.com/

• Microsoft XNA blogs

http://blogs.msdn.com/xna/

• All the sample code and resource links:

http://www.robmiles.com

• Very Silly Games and book links:

http://verysillygames.com